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Avalanche Forecast

Archived

Mar 29th, 2021–Mar 30th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Columbia.

Storm slabs may remain reactive to human triggers as natural avalanche activity tapers off. Start with small terrain features, look for sign of instability and gather information before considering bigger terrain.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Monday night: Partly cloudy. Moderate to strong northwest wind. Freezing level valley bottom. Alpine temperature -12.

Tuesday: Mostly cloudy. Light westerly wind. Freezing level 1500 m. Alpine temperature -7.

Wednesday: Sunny. Light southwest wind. Freezing level 2100 m. Alpine temperature -1.

Thursday: Mix of sun and cloud. Moderate southwest wind. Freezing level 2100 m. Alpine temperature -1.

Avalanche Summary

Preliminary reports of avalanche activity during the storm include several natural, explosive and skier controlled storm slabs averaging size 1-1.5 in the Monashees and at Revelstoke.

Notable reports of avalanche activity prior to the storm include:

  • On Saturday, several natural cornice falls triggered size 2-3 avalanches. One of which is suspected to have run on a deeply buried crust near the base of the snowpack. 
  • On Thursday a natural size 3 was observed on a east aspect at 1800 m in the Valhallas. The crown was 100 cm thick, but no other details are known.

Snowpack Summary

The weekend's storm dropped 20-50 cm over the Selkirk mountains and 10-20 cm in the Monashees. This snow came with wind from southwest to northwest, loading thick slabs in lee features at upper elevations. Reports from Monday have indicated that the new snow is bonding well with underlying surfaces. Crusty and/or moist surfaces exist below treeline depending on elevation and time of day.

At alpine and treeline elevations, a few layers of note are buried 50-100 cm deep including a layer of small surface hoar crystals on shady, wind-sheltered aspects and a series of crusts on solar aspects and below 1800 m. Overall the snow seems to be bonding well to these interfaces, although there have been a few isolated avalanches running on crusts layer over the past few days.

Terrain and Travel

  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Start with conservative lines and watch for clues of instability.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.